The expansion of the cable television industry has vastly changed the amount and quality of the television programming available to the viewing public. Many of the programs now available to a cable subscriber are not suitable for young viewers being replete with graphic violence, sex and language. At the same time, broadcast television has also become more permissive in the amount of similar programming being provided on the air waves.
Although expanded programming provides many advantages to adult viewers, it provides many disadvantages to parents of impressionable children and younger teenagers. Without supervision, parents can find their children watching objectionable programming on either broadcast television channels or on the cable, if available in the household. Parents may try one of several means of physically disabling the television set while their children are unsupervised. Such methods may include removal of the power cord or the remote controller for the television, or disconnection of the antenna leads. Clever young viewers may be able to circumvent these methods by merely reconnecting the power cord, searching and finding the missing control device or reattaching the antenna leads. Further, these methods completely deny younger viewers of television programming, including programming which may have some beneficial informational or educational content.
Subscriber television companies have tried filters in the cable transmission lines and expensive scramblers on both cable and broadcast signals. Besides the expense, such devices have proven ineffective and to a major extent uncontrollable. For example, the parents themselves may have defeated these devices for convenience or other reasons.
Other areas of the communications field also suffer from problems connected with the numerous signals being broadcast. These problems are especially acute in areas where a single transmitter or several transmitters are cluttering the air waves with multiple transmissions. For example, a police precinct may be transmitting signals which are received by a number of police cars tuned in to that frequency even though only a limited number of such police cars may be in need of the specific information being transmitted. In this system, each and every police car must nevertheless receive the communication on its receiver, and listen to it to before deciding whether the information is applicable to their situation.
A similar problem to that of the police precinct is that found around airports. Normally, all traffic is on one or two specific frequencies, such that all planes on a selected frequency must hear the broadcast instructions, which may cause major distractions in the cockpit.
Thus, a need has arisen for a means for electronically limiting the reception of transmitted communications, such as radio, broadcast television and cable television transmissions. Such a system would allow only a specified group of receivers to actually receive and process a transmitted communication. Such a system should be inexpensive and be capable of being integrated into present communications transmitters and receivers.